Light-Induced Passivation of Si by Iodine Ethanol Solution

Abstract

We report on our observations of light-activated passivation (LIP) of Si surfaces by iodine-ethanol (I-E) solution. Based on our experimental results, the mechanism of passivation appears to be related to dissociation of iodine by the photo-carriers injected from the Si wafer into the I-E solution. The ionized iodine (I -) then participates in the formation of a Si-ethoxylate bond that passivates the Si surface. Experiments with a large number of wafers of different material parameters indicate that under normal laboratory conditions, LIP can be observed only in some samples-samples that have moderate minority-carrier lifetime. We explain this observation and also show that wafer cleaning plays an extremely important role in passivation.

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

“…In this regard, illumination is necessary to dissociate I 2 into I − ions which can then remove the hydrogen from the silicon surface. The silicon surface can then “oxidise” another iodine atom, thus forming SiI bonds . The SiI bonds are susceptible to nucleophilic attack by methanol/ethanol, meaning they are prone to attack by the methanol/ethanol solvents, this results in a silicon surface which is preferentially terminated by methoxy or ethoxy.…”

“…Illumination whilst silicon is immersed in I‐E or I‐M solutions has been shown to reduce the time required to reach maximum surface passivation dramatically . In this regard, illumination plays two roles in I‐E and I‐M passivation (i) dissociation of I 2 molecules into I − atoms and (ii) generation of photoexcited carriers in the silicon material which can further enhance surface reactions.…”

“…In general, the standard RCA clean and HF dip prior to I‐E or I‐M passivation has proved to be a good surface pre‐treatment, where in one case a very low S of 0.75 cm s −1 was attained . In contrast there have been reports that indicate a piranha etch (H 2 SO 4 :H 2 O 2 ) or silicon etch (HF:HNO 3 ) prior to halogen‐alcohol passivation provide clean/smooth silicon surface, resulting in S of 1 to 10 cm s −1 …”

Studies on the use of liquid surface passivation for lifetime measurements on good-quality silicon wafers

“…This increase is observed in some p-type wafers with IE passivation. This is due to light-induced passivation (LIP) of the Si surface [7], where additional electrons are generated from the passivant when the sample is illuminated. The lifetime degraded on all of our n-type wafers passivated with IE and illuminated under a solar simulator.…”

Al+Si Interface Optical Properties Obtained in the Si Solar Cell Configuration

“…The formation of the AlþSi interface in commercial solar cells is complex and is the subject of several reports in the literature. [8,9] This distinct AlþSi interface region forms during exposure to high temperatures in typical solar cell fabrication processes, influenced by both silicide formation and heterogeneous mixing of Al and Si. Substantial differences in optical properties of the AlþSi alloy are observed before and after annealing.…”